In an electric device such as a switchgear, a wire-wound type voltage transformer is used for protecting a main circuit or measuring in the main circuit. Recently, an optical voltage transformer that provides advantages, such as anti-inductance, broad spectrum and electric insulation, is widely used.
As this sort of an optical voltage transformer, known is an optical voltage transformer that includes a main circuit section filled with insulation gas, a voltage dividing capacitor connected with the main circuit section, and an optical sensor with electro-optic element. An optical potential transducer disclosed in a Patent Document 1 shown below is an equivalent device to an optical voltage transformer. The optical potential transducer includes a voltage divider for dividing voltage to be measured, and an optical sensor for transducing an output voltage from the voltage divider into optical intensity corresponding to the output voltage by applying the output voltage to an electro-optic crystal. The voltage divider in the optical potential transducer is composed of a voltage divider main section, as a gas capacitor, that is composed of a charged portion to which the measured voltage is applied, a single void electrode surrounding the charged portion and insulation media, and a solid capacitor connected with the void electrode and the optical sensor.
Since the divider main section is composed only of the gas capacitor at the high-tension side and electrical capacity at the low-tension side is ensured by the solid capacitor, a most-outer void electrode that was previously needed can be omitted and thereby downsizing and weight-saving of the voltage divider can be achieved.
In addition, an optical voltage transformer disclosed in a Patent Document 2 shown below includes a main circuit section that has a ceramic capacitor instead of insulation gas, another ceramic capacitor connected with the main circuit section for dividing voltage, and an optical sensor having an electro-optic element. These components are integrally molded to be surrounded with an insulation layer.
According to the optical voltage transformer, since the capacitor for dividing voltage and the optical sensor are integrally molded with the insulation material, downsizing can be achieved and its handling upon being attached onto a conductor to be measured can be easy.    Patent Document 1: Japanese Patent Application Laid-open No. Hei 7-83961    Patent Document 2: Japanese Patent Application Laid-open No. Hei 11-202000